The gelatinous cube, b, is an amoeboidmonster in NetHack. Unlike the Dungeons & Dragons creature from which it is derived, it has no means to engulf the player; however it still possesses the means to paralyze the unwary. The gelatinous cube possesses two different kinds of attacks that may paralyze the player. The paralyzing touch is a melee attack that can be protected against with high magic cancellation. It also has a paralyzing passive attack which can be prevented by wearing a ring of free action or not engaging in melee combat. Their corpses are acidic, but may also provide fire/cold/shock/sleep resistance.

Gelatinous cubes are noteworthy in that as they move they will eat organic items they pass over and engulf most other items (exceptions being rocks or a punished player's iron ball and chain) which are then placed into the cube's inventory. They are thus useful for cleaning useless items out of a level, and the bane of stashes.